The present invention relates to a liquid crystal display device used for a liquid crystal projector.
A liquid crystal projector displays an image through a transmission liquid crystal display panel, enlarges and projects the image displayed on the panel through a projection lens onto a screen, and is constructed as described below.
FIG. 1 is a view for illustrating a principle of a conventional liquid crystal projector. In FIG. 1, projection lens 2, associated with a plurality of optical lenses, is provided on the front surface of projector case 1. Transmission dot matrix liquid crystal display panel 3 is opposed to lens 2 in case 1. Light source 4 is provided behind panel 3 in case 1, and has light source lamp 5 and reflector 6 for reflecting the light emitted from lamp 5 toward the back surface of panel 3. Infrared ray components are removed by infrared ray-removing filter (an infrared ray reflection or absorption filter) 7 from the light of light source 4, and the light is incident to panel 3. The light transmitted through panel 3 and hence the displaying image of panel 3 is condensed by condensing lens 8, enlarged by lens 2, and projected onto screen 9.
More particularly, this projector enlarges the image displayed on the liquid crystal display panel, and projects the image on the screen. According to the projector, the image displayed on the display panel, which has a small screen size, can be enlarged to be easily observed. The prior art of such a liquid crystal projector is disclosed in U.S. Pat. No. 3,895,866.
In the above-mentioned liquid crystal projector, panel 3 is heated by infrared ray components of the light incident to panel 3 (because the infrared ray components of the light emitted from light source 4 to panel 3 is removed by filter 7 to some degree but not completely removed). Further, since panel 3 is heated by the temperature rise in case 1 due to the heat radiated from light source 4, the liquid crystal temperature in panel 3 rises to thereby cause the display contrast of panel 3 to decrease. Thus, there arise problems that a clear image cannot be projected on screen 9 and the lifetime of the liquid crystal in panel 3 is reduced. The temperature rise in case 1 can be suppressed to some degree by ventilation, but a xenon or halongen lamp of high luminance, generally used as lamp 5 of the liquid crystal projection, radiates considerable heat. Therefore, the temperature rise in case 1 cannot be effectively suppressed only by ventilation to reduce thermal influence to panel 3.